The organization of cutaneous receptor of different types in terms of their segregation and interactions in central nervous system relays is to be studied at several levels, extending from sensory ganglion afferents to cerebral cortex, with principal emphasis on the trigeminal system. Anatomical methods will be employed to examine 1) the central and peripheral terminal branching pattern in single ganglion cells labeled intracellularly by iontophoretic injection of horseradish peroxidase (HRP) and labeling of ganglion cells by peripheral receptor application with HRP; 2) connections of the trigeminal ganglion and the main subdivisions of the sensory trigeminal nucleus complex will be analyzed for intranuclear organization as well as ascending and peripheral interactions by focal injection of a) tritiated amino acids and nucleosides, and b) HRP incubated with new sensitive substrates; 3) thalamic and cortical modality segregation determined by electrophysiological methods will be studied with focal HRP injection; 4) the central projections of specific trigeminal receptors will be excited by natural stimulation during systemic injection of a metabolic marker, 2-deoxyglucose, the localized accumulation of which will be detected with a new method under development utilizing a tritium label and fixed tissue. Electrophysiological experiments will continue with 1) an analysis of modality segregation in the cat thalamus (VB) with horizontal and sagittal penetrations; 2) quantitative analysis of VB neurons with emphasis on complex spatial properties; 3) cortical mapping of neurons for a single vibrissa in rat and cat, and 4) quantitative analysis of first-order sensitive mechanoreceptors in relation to peripheral terminals and for comparison with central neurons.